Power conversion equipment

ABSTRACT

Power conversion equipment has a first input terminal and a second input terminal to which an AC input voltage is applied, a plurality of AC-DC converters which are series-connected between the first input terminal and the second input terminal and each of which converts a divided input voltage obtained by dividing the input voltage into a full-wave rectified voltage in a state of being insulated electrically, and a first output terminal and a second output terminal through which the full-wave rectified voltages converted by the plurality of AC-DC converters are output commonly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2018-198717, filed on Oct. 22,2018, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments of the present disclosure relate to power conversionequipment.

BACKGROUND

Power conversion equipment such as an AC-DC converter and a DC-DCconverter is proposed which performs a power conversion by applying aninput voltage to a multi-cell circuit in which a plurality of cellcircuits are connected in series. In this kind of power conversionequipment, generally, a slave controller which controls an outputvoltage or an output current of each cell circuit is provided in each ofthe cell circuits, and a master controller is provided which stabilizesthe operation of all the cell circuits in the multi-cell circuit. Themaster controller needs to control each cell circuit in cooperation witheach slave controller, and thus the control becomes complicated. Inaddition, when the master controller is provided, the number ofcomponents increases, and further a wiring for connecting the mastercontroller and all the cell circuits is required so as to increase thenumber of wirings. Thus, power consumption is increased, andminiaturization also becomes difficult.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of power conversion equipment according to afirst embodiment;

FIG. 2A is a view illustrating a voltage waveform of an input voltageand a divided input voltage, FIG. 2B is a view illustrating a voltagewaveform of a full-wave rectified voltage, and FIG. 2C is a viewillustrating a voltage waveform of an output voltage of a DC-DCconverter;

FIG. 3A is a view in which a direction of a current flowing in eachAC-DC converter is indicated by an arrow in a case where a divided inputvoltage has a positive polarity;

FIG. 3B is a waveform diagram illustrating on/off timings of first tofourth transistors and a current waveform of an inductor 4 in each AC-DCconverter in a case where the divided input voltage has a positivepolarity;

FIG. 4 is a waveform diagram illustrating an aspect in which the currentwaveform w5 of the inductor 4 in each AC-DC converter in a case wherethe divided input voltage has a positive polarity is changed;

FIG. 5A is a view in which a direction of a current flowing in eachAC-DC converter 2 is indicated by an arrow in a case where the dividedinput voltage is a negative polarity;

FIG. 5B is a view illustrating on/off timings of the first to fourthtransistors and a current waveform of the inductor 4 in each AC-DCconverter in a case where the divided input voltage has a negativepolarity;

FIG. 6 is a waveform diagram illustrating an aspect in which a currentwaveform w5 of the inductor 4 in each AC-DC converter in a case wherethe divided input voltage has a negative polarity is changed;

FIG. 7 is a waveform diagram illustrating a simulation result of thepower conversion equipment of FIG. 1;

FIG. 8 is a view illustrating an example in which a DC-DC converter isconnected to a first output terminal and a second output terminal in thepower conversion equipment of FIG. 1;

FIG. 9 is a view illustrating an example in which a DC-AC inverter isprovided in the power conversion equipment; and

FIG. 10 is a circuit diagram of power conversion equipment according toa second embodiment.

DETAILED DESCRIPTION

According to one embodiment, power conversion equipment has a firstinput terminal and a second input terminal to which an AC input voltageis applied, a plurality of AC-DC converters which are series-connectedbetween the first input terminal and the second input terminal and eachof which converts a divided input voltage obtained by dividing the inputvoltage into a full-wave rectified voltage in a state of being insulatedelectrically, and a first output terminal and a second output terminalthrough which the full-wave rectified voltages converted by theplurality of AC-DC converters are output commonly.

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. In the following embodiments, thedescription will be given mainly about characteristic configurations andoperations in power conversion equipment. However, the power conversionequipment may include configurations and operations omitted in thedescriptions below.

First Embodiment

FIG. 1 is a circuit diagram of power conversion equipment 1 of a firstembodiment. The power conversion equipment 1 of FIG. 1 includes a firstinput terminal In1 and a second input terminal In2, a plurality of AC-DCconverters 2, and a first output terminal Out1 and a second outputterminal Out2.

An AC input voltage Vin is applied to a first input terminal In1 and asecond input terminal In2. More specifically, with the voltage of one ofthe first input terminal In1 and the second input terminal In2 as areference, the input voltage Vin is applied to the other. For example,one of the first input terminal In1 and the second input terminal In2 isset as a ground potential as a reference.

Respective input terminals of a plurality of AC-DC converters 2 areseries-connected between the first input terminal In1 and the secondinput terminal In2. For this reason, a divided input voltage Vdinobtained by dividing the input voltage Vin is applied to each AC-DCconverter 2. In the state of being insulated electrically, the AC-DCconverter 2 converts the divided input voltage Vdin into a full-waverectified voltage Vr (Vr=K×|Vdin|, K is a fixed number depending on thecircuit configuration or the connection number of the AC-DC converter 2,the winding ratio of a transformer 3 configuring the AC-DC converter 2,and the like). The full-wave rectified voltage Vr converted by eachAC-DC converter 2 is output from the common first output terminal Out1and second output terminal Out2. That is, the respective outputterminals of the plurality of AC-DC converters 2 are connected inparallel with the first output terminal Out1 and the second outputterminal Out2. FIG. 2A illustrates a voltage waveform of the inputvoltage Vin and the divided input voltage Vdin, and FIG. 2B illustratesa voltage waveform of the full-wave rectified voltage Vr. The inputvoltage Vin and the divided input voltage Vdin have the same frequency.The full-wave rectified voltage Vr mainly has a DC component and twotimes of the frequency of the input voltage Vin and the divided inputvoltage Vdin.

In this way, the power conversion equipment 1 of FIG. 1 includes aplurality of AC-DC converters 2 which have parallel outputs and a serialinput. The plurality of AC-DC converters 2 configure a multi-cellcircuit, and each AC-DC converter 2 configures a cell circuit. Thenumber of connection stages of the AC-DC converters 2 in the powerconversion equipment 1 is not limited. The number of the connectionstages of the AC-DC converters 2 may be determined by taking intoconsideration the voltage amplitude of the input voltage Vin, thebreakdown voltage of the switching element in the AC-DC converter 2, orthe like.

The voltage amplitude of the input voltage Vin and the voltage amplitudeof the full-wave rectified voltage Vr are not particularly limited. Forexample, a commercial AC voltage of 100 V or 200 V may be set as theinput voltage Vin. The full-wave rectified voltage Vr can be also set toan optional voltage amplitude by changing the voltage conversion ratioof the AC-DC converter 2.

The internal configuration of each AC-DC converter 2 is not limitedparticularly. However, the internal configuration of the AC-DC converter2 of FIG. 1 is described as one example. Each AC-DC converter 2 of FIG.1 includes a first capacitor C1, first to fourth transistors Q1 to Q4, atransformer 3, an inductor 4, a second capacitor C2, a diode bridgecircuit 5, a third capacitor C3, and a local controller (controlcircuit) 6.

The first to fourth transistors Q1 to Q4 are cascode-connected between afirst node n1 and a second node n2 to which the divided input voltageVdin is applied. For example, the first to fourth transistors Q1 to Q4are n-type power MOSFETs. In each of the first to fourth transistors Q1to Q4, a diode 7 is parallel-connected between a drain and a source.Gate voltages of the first to fourth transistors Q1 to Q4 are controlledby a local controller 6. The diode 7 may use a body diode of the powerMOSFET.

One end of the inductor 4 is connected to the connection path of asecond transistor Q2 and a third transistor Q3. The other end of theinductor 4 is connected to one end of a primary coil 3 a of thetransformer 3. One end of the second capacitor C2 is connected to theother end of the primary coil 3 a of the transformer 3. The other end ofthe second capacitor C2 is connected to the second node n2.

The transformer 3 includes the primary coil 3 a and a secondary coil 3 bwhich are coupled magnetically in the state of being insulatedelectrically. Thus, a primary circuit from the first node n1 and thesecond node n2 to the primary coil 3 a and a secondary circuit from thesecondary coil 3 b to the first output terminal Out1 and the secondoutput terminal Out2 are insulated electrically. The diode bridgecircuit 5 including first to fourth diode D1 to D4 is connected to thesecondary coil 3 b of the transformer 3. An output end of the diodebridge circuit 5 is connected to the first output terminal Out1 and thesecond output terminal Out2. In addition, the third capacitor C3 isconnected between the first output terminal Out1 and the second outputterminal Out2.

The local controller 6 turns on or off the first to fourth transistorsQ1 to Q4 according to the polarity of the divided input voltage Vdin.More specifically, in a case where the divided input voltage Vdin has apositive polarity, the local controller 6 always turns on the secondtransistor Q2 and the fourth transistor Q4 and performs a switchingoperation of repeatedly turning on and off the first transistor Q1 andthe third transistor Q3 at a constant duty ratio (for example, 0.5) andcomplementarily. In addition, in a case where the divided input voltageVdin has a negative polarity, the local controller 6 always turns on thefirst transistor Q1 and the third transistor Q3 and performs a switchingoperation of repeatedly turning on and off the second transistor Q2 andthe fourth transistor Q4 at a constant duty ratio (for example, 0.5) andcomplementarily. The local controller 6 is used to turn on or off thefirst to fourth transistors Q1 to Q4 of the AC-DC converter 2 to whichthe local controller 6 is connected, and it is not necessary tosynchronize with the local controller connected to another AC-DCconverter 2 and to exchange the information.

In the power conversion equipment 1 according to the present embodiment,each AC-DC converter 2 includes the local controller 6 but does notinclude a master controller which overall controls the plurality ofAC-DC converters 2. This is because the plurality of AC-DC converters 2connected in series have a property that performs automatically anoperation of balancing the input voltage and the output current of eachAC-DC converter 2 even without performing the overall control in a casewhere the first to fourth transistors Q1 to Q4 are turned on/off at aconstant duty ratio, and the input/output voltage of the AC-DC converter2 has a full-wave rectified waveform or becomes Vr=K×|Vdin|. If themaster controller is provided to overall control each AC-DC converter 2as in the related art, each slave controller necessarily changes thecontrol as a result, and further an operation that the master controllerchanges the control again is repeated. Thus, the control becomescomplicated, and the operation of each AC-DC converter 2 becomesunstable, which is a concern.

In each local controller 6 in the present embodiment, only a simplecontrol is performed which switches between on and off of the first tofourth transistors Q1 to Q4 at a constant duty ratio depending onwhether the input voltage Vdin has a positive polarity or a negativepolarity. Any additional controls are not performed such as a control ofchanging the duty ratio such that a voltage or a current follows acertain command value. Accordingly, the input voltage and the outputcurrent of each of the AC-DC converters 2 connected in series arebalanced automatically, and as a result, the operation of each AC-DCconverter 2 is stabilized. In addition, it is possible to match thevoltage amplitudes, the frequencies, and the phases of the full-waverectified voltages Vr output from the AC-DC converters 2.

FIG. 3A is a view in which the direction of the current flowing in eachAC-DC converter 2 is indicated by an arrow in a case where the dividedinput voltage Vdin has a positive polarity, and FIG. 3B is a waveformdiagram illustrating the on/off timing of the first to fourthtransistors Q1 to Q4 and a current waveform w5 of a resonance circuit ineach AC-DC converter 2 in a case where the divided input voltage Vdinhas a positive polarity. FIG. 3B illustrates a waveform diagram within aperiod of about 11 μs in a case where a switching frequency of the firstto fourth transistors Q1 to Q4 is set to 500 kHz. However, a waveformdiagram of FIG. 3B continues during a period (for example, for 10 mswhen the frequency of the divided input voltage Vdin is 50 Hz) in whichthe divided input voltage Vdin is positive.

In a case where the divided input voltage Vdin has a positive polarity,the local controller 6 performs a switching operation that always turnson the second transistor Q2 and the fourth transistor Q4 and repeatedlyturns on and off the first transistor Q1 and the third transistor Q3 ata constant duty ratio (a duty ratio is equal to or more than 0 and equalto or less than 0.5, for example, 0.5) and complementarily. Thus, asillustrated in FIG. 3A, in a case where the first transistor Q1 isturned on, a current flows in a direction of the first node n1→thedrain-source of the first transistor Q1→the source-drain of the secondtransistor Q2 and the diodes 7 connected in parallel→the inductor 4→a DCoutput circuit including the primary coil 3 a and the secondary coil 3 bof the transformer 3, the diode bridge 5, and the third capacitor C3→thesecond capacitor C2→the second node n2. In a case where the thirdtransistor Q3 is turned on, a current flows in a direction of theinductor 4→the third transistor Q3→the source-drain of the fourthtransistor Q4 and the diode 7→the second capacitor C2→the DC outputcircuit including the primary coil 3 a and the secondary coil 3 b of thetransformer 3, the diode bridge 5, and the third capacitor C3. Inaddition, in a state where the first transistor Q1 and the thirdtransistor Q3 are each turned on, a resonance circuit is configured toinclude the inductor 4 and the second capacitor C2. In the resonancecircuit, a current flows which resonates at a resonance frequencydetermined by the inductance of the inductor 4 and the capacity of thesecond capacitor C2. At the timing when the polarity of the currentresonating at the resonance frequency is inverted, the switchingoperation of the first transistor Q1 and the third transistor Q3 isperformed, or the inductance of the inductor 4 and the capacity of thesecond capacitor C2 are determined for matching with the switchingfrequency of the first transistor Q1 and the third transistor Q3. Theinductance of the inductor 4 and the capacity of the second capacitor C2are adjusted such that the resonance frequency becomes a frequencyfaster than the frequency of the input voltage Vin.

In FIG. 3A, a current path in a case where the divided input voltageVdin has a positive polarity, the first transistor Q1 is turned on, andthe third transistor Q3 is turned off is indicated by a solid-linearrow, and a current path in a case where the divided input voltage Vdinhas a positive polarity, the first transistor Q1 is turned off, and thethird transistor Q3 is turned on is indicated by a broken-line arrow. Asillustrated in the drawing, when the first transistor Q1 and the thirdtransistor Q3 are complementarily turned on/off, the direction of thecurrent flowing through the resonance circuit including the inductor 4and the second capacitor C2 is changed, and thus the direction of thecurrent flowing through the secondary coil 3 b of the transformer 3 ischanged. However, since the diode bridge circuit 5 is provided, thepolarity of the output voltage Vr of the AC-DC converter 2 is notchanged.

When the primary coil 3 a and the secondary coil 3 b of the transformer3 have reverse winding directions, in a case where the voltage appliedto between the drain terminal of the third transistor Q3 and the drainterminal of the fourth transistor Q4 is positive, an induced current isgenerated in a direction of a second diode D2→the secondary coil 3 b→athird diode D3. In a case where the voltage applied to between the drainterminal of the third transistor Q3 and the drain terminal of the fourthtransistor Q4 is zero, an induced current is generated in a direction ofthe fourth diode D4→the secondary coil 3 b→the first diode D1.

FIG. 4 is a waveform diagram illustrating an aspect in which the currentwaveform w5 of the inductor 4 in each AC-DC converter 2 in a case wherethe divided input voltage Vdin has a positive polarity is changed. Asillustrated in FIG. 4, while the divided input voltage Vdin has apositive polarity, a resonance current having an amplitude proportionalto the amplitude of the divided input voltage Vdin flows through theinductor 4 by complementarily turning on/off the first transistor Q1 andthe third transistor Q3 at a constant duty ratio.

FIG. 5A is a view in which the direction of the current flowing in eachAC-DC converter 2 is indicated by an arrow in a case where the dividedinput voltage Vdin has a negative polarity, and FIG. 5B is a viewillustrating the on/off timing of the first to fourth transistors Q1 toQ4 and the current waveform w5 of the resonance circuit in each AC-DCconverter 2 in a case where the divided input voltage Vdin has anegative polarity. FIG. 5B illustrates a waveform diagram within aperiod of about 11 μs in a case where a switching frequency of the firstto fourth transistors Q1 to Q4 is set to 500 kHz. However, a waveformdiagram of FIG. 5B continues during a period (for example, for 10 mswhen the frequency of the divided input voltage Vdin is 50 Hz) in whichthe divided input voltage Vdin is negative. In a case where the dividedinput voltage Vdin has a negative polarity, the local controller 6performs a switching operation that always turns on the first transistorQ1 and the third transistor Q3 as illustrated in FIG. 5A and repeatedlyturns on and off the second transistor Q2 and the fourth transistor Q4at a constant duty ratio (for example, 0.5) and complementarily. Thus,as illustrated in FIG. 5B, in a case where the second transistor Q2 isturned on, a current flows in a direction of the second node n2→thesecond capacitor C2→the DC output circuit including the primary coil 3 aand the secondary coil 3 b of the transformer 3, the diode bridge 5, andthe third capacitor C3→the inductor 4→the drain-source of the secondtransistor Q2→the source-drain of the first transistor Q1 and the diode7 connected in parallel between the drain-source of the first transistorQ1→the first node n1. In a case where the fourth transistor Q4 is turnedon, a current flows in a direction of the inductor 4→the DC outputcircuit including the primary coil 3 a and the secondary coil 3 b of thetransformer 3, the diode bridge 5, and the third capacitor C3→the secondcapacitor C2→the fourth transistor Q4→the source-drain of the thirdtransistor Q3 and the diode 7 connected between the drain-source of thethird transistor Q3. In addition, in a state where the second transistorQ2 and the fourth transistor Q4 are each turned on, a resonance circuitis configured to include the second capacitor C2 and the inductor 4. Inthe resonance circuit, a current flows which resonates at a resonancefrequency determined by the inductance of the inductor 4 and thecapacity of the second capacitor C2.

In FIG. 5A, a current path in a case where the divided input voltageVdin has a negative polarity, the second transistor Q2 is turned on, andthe fourth transistor Q4 is turned off is indicated by a solid-linearrow, and a current path in a case where the divided input voltage Vdinhas a negative polarity, the second transistor Q2 is turned off, and thefourth transistor Q4 is turned on is indicated by a broken-line arrow.As illustrated in the drawing, when the first transistor Q1 and thethird transistor Q3 are complementarily turned on/off, the direction ofthe current flowing through the resonance circuit including the inductor4 and the second capacitor C2 is changed, and thus the direction of thecurrent flowing through the secondary coil 3 b of the transformer 3 ischanged. However, since the diode bridge circuit 5 is provided, thepolarity of the output voltage Vr of the AC-DC converter 2 is notchanged.

FIG. 6 is a waveform diagram illustrating an aspect in which the currentwaveform w5 of the inductor 4 in each AC-DC converter 2 in a case wherethe divided input voltage Vdin has a negative polarity is changed. Asillustrated in FIG. 6, while the divided input voltage Vdin has anegative polarity, a resonance current having an amplitude proportionalto the amplitude of the divided input voltage Vdin flows through theinductor 4 by complementarily turning on/off the second transistor Q2and the fourth transistor Q4 at a constant duty ratio.

FIG. 7 is a waveform diagram illustrating a simulation result of thepower conversion equipment 1 of FIG. 1. In the simulation of FIG. 7, anexample is illustrated in which three AC-DC converters 2 are connectedbetween the first input terminal In1 and the second input terminal In2.

A waveform w1 of FIG. 7 is a waveform of the input voltage Vin of AC 100V at 50 Hz. A waveform w2 is a waveform of the divided input voltageVdin applied to each AC-DC converter 2. A waveform w3 is a waveform ofthe full-wave rectified voltage Vr. A waveform w4 is a waveform of acurrent flowing through the resonance circuit in each AC-DC converter 2.The waveform w5 is a waveform obtained by enlarging an area within aframe w6 of the waveform w4 in a time-axis direction. As illustrated inthe drawing, the resonance circuit performs a resonance operation at aresonance frequency (for example, about 500 kHz) much faster than thefrequency of the input voltage Vin. The resonance frequency of theresonance circuit can be adjusted by the inductance of the inductor 4and the capacity of the second capacitor C2.

As understood from the simulation result of FIG. 7, the power conversionequipment 1 of FIG. 1 outputs the full-wave rectified voltage Vrillustrated in the waveform w3 in synchronization with the frequency ofthe input voltage Vin illustrated in the waveform w1. The phase of thepeak position of the full-wave rectified voltage Vr matches with thephase of the peak position of the input voltage Vin. In addition, thedivided input voltage Vdin illustrated in the waveform w2 has thevoltage amplitude of about one-third of the input voltage Vin. Further,the voltage amplitude of the full-wave rectified voltage Vr illustratedin the waveform w3 has about a half of the divided input voltage Vdin.This is because the voltage applied to the primary coil 3 a of thetransformer 3 through the second capacitor C2 is set to −Vdin/2 and+Vdin/2 while the voltage which first to fourth four transistors Q1 toQ4 connected in cascode output to between the connection node of thesecond transistor Q2 and the third transistor Q3 as a central point andthe node n2 is Vdin and 0.

In the full-wave rectified voltage Vr which is output from the firstoutput terminal Out1 and the second output terminal Out2 in the powerconversion equipment 1 of FIG. 1, even-number higher harmonic wave ofVin is included in the DC voltage. Thus, various kinds of electricapparatuses cannot be driven which requires to receive the supply of theDC voltage which has a small higher harmonic wave and is an almostconstant value. However, some electric apparatuses such as anincandescent lamp can be driven by the full-wave rectified voltage Vr.

FIG. 8 is a view illustrating an example in which the DC-DC converter 10is connected to the first output terminal Out1 and the second outputterminal Out2 in the power conversion equipment 1 of FIG. 1. The DC-DCconverter 10 of FIG. 8 levels the voltage amplitude of the full-waverectified voltage Vr to generate the DC voltage. In actual, asillustrated in FIG. 2C, in some cases, the output voltage Vout of theDC-DC converter 10 of FIG. 8 becomes a DC voltage slightly having aripple component. The ripple component of the output voltage Vout can bereduced by enlarging a fourth capacitor C4.

The internal configuration of the DC-DC converter 10 is not limitedparticularly. However, the configuration of FIG. 8 is described as oneexample. The DC-DC converter 10 of FIG. 8 includes an inductor 11, afifth transistor Q5, a diode 12, an electrolytic capacitor C4, and alocal controller 13. One end of the inductor 11 is connected to thefirst output terminal Out1. The other end of the inductor 11 isconnected to the anode of the diode 12 and the drain of the fifthtransistor Q5. The source of the fifth transistor Q5 is connected to thesecond output terminal Out2. The cathode of the diode 12 is connected tothe third output terminal Out3 and one end of the electrolytic capacitorC4. The other end of the electrolytic capacitor C4 is connected to thesecond output terminal Out2 and the fourth output terminal Out4.Incidentally, the capacitor without a polarity may be connected insteadof the electrolytic capacitor C4.

The turning on/off of the fifth transistor Q5 is controlled by the localcontroller 13. The local controller 13 controls the gate voltage of thefifth transistor Q5 according to the output voltage Vr between the firstoutput terminal Out1 and the second output terminal Out2 and the outputvoltage Vout of the DC-DC converter 10.

Incidentally, the circuit connected to the first output terminal Out1and the second output terminal Out2 in the power conversion equipment 1of FIG. 1 is not necessarily limited to the DC-DC converter 10illustrated in FIG. 8. For example, the DC-AC inverter may be connectedas illustrated in FIG. 9. The power conversion equipment 1 of FIG. 9combines the AC-DC converter 2 and the DC-AC inverter 14 to configure anAC-AC converter.

At least a part of the power conversion equipment 1 of FIG. 1, 8, or 9can be configured by one or a plurality of semiconductors IC. Forexample, each AC-DC converter 2 may be configured by a separatesemiconductor IC. In addition, the transformer 3 may be externallyattached to the semiconductor IC or incorporated in the semiconductorIC. In the case of being incorporated, two facing semiconductor layersmay be each formed to have a conductive pattern having a spiral shape tobe coupled magnetically.

In this way, in the power conversion equipment 1 according to the firstembodiment, the plurality of AC-DC converters 2 are series-connectedbetween the first input terminal In1 and the second input terminal In2to which the input voltage Vin is applied, the output terminal of eachof the plurality of AC-DC converters 2 is configured to be connected inparallel with the first output terminal Out1 and the second outputterminal Out2, and the local controller 6 is provided in each AC-DCconverter 2 to control a timing of turning on or off the first to fourthtransistors Q1 to Q4 in each AC-DC converter 2. However, the mastercontroller is not provided which overall controls the plurality of AC-DCconverters 2. The operation is performed which automatically balancesthe input voltage Vdin and the output current of each AC-DC converter 2without the master controller. Thus, compared to the related art, theplurality of AC-DC converters can be operated stably with a simplecontrol. In addition, compared to the related art, the number ofcomponents and the number of the wirings are reduced. Thus, it ispossible to reduce a component cost and a consumption power and torealize miniaturization.

Second Embodiment

In a second embodiment, each AC-DC converter 2 is simplified further.

FIG. 10 is a circuit diagram of the power conversion equipment 1according to the second embodiment. Similarly with FIG. 1, in the powerconversion equipment 1 of FIG. 10, the plurality of AC-DC converters 2are series-connected between the first input terminal In1 and the secondinput terminal In2, and the output voltages of the AC-DC converters 2are connected in parallel and output from the common first outputterminal Out1 and second output terminal Out2. The internalconfiguration of each AC-DC converter 2 of FIG. 10 is different from theinternal configuration of the AC-DC converter 2 of FIG. 1.

Each AC-DC converter 2 in FIG. 10 includes a diode bridge circuit 15,the first capacitor C1, the first transistor Q1, the second transistorQ2, the inductor 4, the second capacitor C2, the transformer 3, thediode bridge circuit 5, the third capacitor C3, and the local controller6.

The divided input voltage Vdin is applied to the diode bridge circuit15. The diode bridge circuit 15 including fifth to eighth diodes D5 toD8 converts the divided input voltage Vdin into the first full-waverectified voltage. The first full-wave rectified voltage is applied tobetween the first node n1 and the second node n2. The first capacitor C1is connected between the first node n1 and the second node n2, and thefirst transistor Q1 and the second transistor Q2 are cascode-connected.One end of the inductor 4 is connected to the connection path of thefirst transistor Q1 and the second transistor Q2. The connectionrelation of the inductor 4, the primary coil 3 a of the transformer 3,and the second capacitor C2 is similar with that of FIG. 1. One end ofthe second capacitor C2 is connected to the source of the secondtransistor Q2.

In this way, each AC-DC converter 2 of FIG. 10 has the first and secondtransistors Q1 and Q2 of which the number is smaller than that of FIG. 1by two. In the local controller 6 of FIG. 10, for example, a duty ratiois set to 50% (the duty ratio is 0.5), and the first transistor Q1 andthe second transistor Q2 are alternately turned on. The local controller6 may alternately turn on/off the first transistor Q1 and the secondtransistor Q2 regardless of the positive or negative polarity or thephase of the input voltage Vin. The local controller 6 of FIG. 1 turnson or off the first to fourth transistors Q1 to Q4 depending on whetherthe input voltage Vin has a positive polarity or a negative polarity.However, the local controller 6 of FIG. 10 can control the turningon/off of the first transistor Q1 and the second transistor Q2 with asimple control compared to the control of the local controller 6 of FIG.1.

The local controller 6 performs the switching operation of repeatedlyturning on and off the first transistor Q1 and the second transistor Q2at a constant duty ratio (for example, 0.5). In a case where the dividedinput voltage Vdin has a positive polarity, while the first transistorQ1 is turned on, a current flows in a direction of the first node n1→thedrain-source of the first transistor Q1→the inductor 4→the DC outputcircuit including the primary coil 3 a and the secondary coil 3 b of thetransformer 3, the diode bridge 5, and the third capacitor C3→the secondcapacitor C2→the second node n2. In addition, while the secondtransistor Q2 is turned on, a current flows in a direction of theinductor 4→the drain-source of the second transistor Q2→the secondcapacitor C2→the DC output circuit including the primary coil 3 a andthe secondary coil 3 b of the transformer 3, the diode bridge 5, and thethird capacitor C3. The resonance circuit including the inductor 4 andthe second capacitor C2 performs the resonance operation at apredetermined resonance frequency, and thus the first transistor Q1 andthe second transistor Q2 perform the switching operation at a frequencyequal to the resonance frequency determined by the inductance of theinductor 4 and the capacity of the second capacitor C2.

On the other hand, also in a case where the divided input voltage Vdinhas a negative polarity, by a rectifying operation of the diode bridgecircuit 15, each AC-DC converter 2 of FIG. 10 performs the same circuitoperation as in a case where the divided input voltage Vdin has apositive polarity. While the first transistor Q1 is turned on, a currentflows in a direction of the first node n1→the drain-source of the firsttransistor Q1→the inductor 4→the DC output circuit including the primarycoil 3 a and the secondary coil 3 b, the diode bridge 5, and the thirdcapacitor C3→the second capacitor C2→the second node n2. In addition,while the second transistor Q2 is turned on, a current flows in adirection of the second capacitor C2→the DC output circuit including theprimary coil 3 a and the secondary coil 3 b of the transformer 3, thediode bridge 5, and the third capacitor C3→the inductor 4→thedrain-source of the second transistor Q2.

In this way, in each AC-DC converter 2 according to the secondembodiment, the diode bridge circuit 15 is newly added differently fromthe AC-DC converter 2 of FIG. 1. However, since two transistors forswitching can be reduced, and it is not necessary to judge the polarityof the divided input voltage Vdin, the control of the local controller 6can be simplified. Accordingly, the internal configuration of each AC-DCconverter 2 can be simplified compared to FIG. 1, and it is possible torealize miniaturization and low power consumption and to reduce thecomponent cost.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

1. Power conversion equipment comprising: a first input terminal and asecond input terminal to which an AC input voltage is applied; aplurality of AC-DC converters which are series-connected between thefirst input terminal and the second input terminal and each of whichconverts a divided input voltage obtained by dividing the input voltageinto a full-wave rectified voltage in a state of being insulatedelectrically; and a first output terminal and a second output terminalthrough which the full-wave rectified voltages converted by theplurality of AC-DC converters are output commonly.
 2. The powerconversion equipment according to claim 1, wherein the plurality ofAC-DC converters convert the divided input voltages into the full-waverectified voltages in synchronization with a frequency of the inputvoltage.
 3. The power conversion equipment according to claim 1, whereineach of the plurality of AC-DC converters comprises: a plurality ofswitching elements which are cascode-connected between a first node anda second node to which the divided input voltage is applied, and acontrol circuit which turns on or off the plurality of switchingelements according to a polarity of the input voltage.
 4. The powerconversion equipment according to claim 3, wherein the plurality ofAC-DC converters automatically balance the input voltage and an outputvoltage without a master controller which totally controls the pluralityof AC-DC converters.
 5. The power conversion equipment according toclaim 3, wherein the plurality of switching elements comprise first,second, third and fourth transistors cascode-connected between the firstinput terminal and the second input terminal, and the control circuitcontrols gate voltages of the first to fourth transistors.
 6. The powerconversion equipment according to claim 5, wherein the control circuitswitches on or off of the first to fourth transistors at a constant dutyratio.
 7. The power conversion equipment according to claim 1, whereineach of the plurality of AC-DC converters comprises: a diode bridgecircuit which converts the divided input voltage into a dividedfull-wave rectified voltage, a plurality of switching elements which arecascode-connected between a first node and a second node to which thedivided full-wave rectified voltage is applied, and a control circuitwhich turns on or off the plurality of switching elements at apredetermined duty ratio.
 8. The power conversion equipment according toclaim 7, wherein the plurality of switching elements comprise first andsecond transistors cascode-connected between the first input terminaland the second input terminal, and the control circuit controls gatevoltages of the first and second transistors.
 9. The power conversionequipment according to claim 8, wherein the control circuit turns on oroff the first and second transistors at a constant duty ratio.
 10. Thepower conversion equipment according to claim 9, wherein the controlcircuit turns on or off the first and second transistors at a constantduty ratio regardless of positive or negative polarity or the phase ofthe input voltage.
 11. The power conversion equipment according to claim1, wherein each of the plurality of AC-DC converters comprises: aprimary circuit which comprises a resonance circuit which resonates at afrequency faster than a frequency of the input voltage insynchronization with a frequency of the input voltage, a secondarycircuit which is electrically insulated from the primary circuit andoutputs the full-wave rectified voltage, and a transformer whichperforms a power conversion from the primary circuit to the secondarycircuit in a state of being insulated electrically.
 12. The powerconversion equipment according to claim 1, further comprising: a DC-DCconverter which is connected to the first output terminal and the secondoutput terminal and converts the full-wave rectified voltage into a DCvoltage.
 13. The power conversion equipment according to claim 1,further comprising: a DC-AC inverter which is connected to the firstoutput terminal and the second output terminal and converts thefull-wave rectified voltage into an AC voltage.